Since the advent of a resist for KrF excimer laser (248 nm), an image forming method called chemical amplification is used as an image forming method for resist so as to compensate for sensitivity reduction caused by light absorption. For example, the image forming method by positive chemical amplification is an image forming method of decomposing an acid generator in the exposed area upon exposure to an excimer laser, an electron beam, extreme-ultraviolet light or the like to produce an acid, converting an alkali-insoluble group into an alkali-soluble group by using the generated acid as a reaction catalyst in the baking after exposure (PEB: Post Exposure Bake), and removing the exposed area with an alkali developer.
As for the alkali developer used in the method above, various alkali developers have been proposed, but an aqueous alkali developer of 2.38mass % TMAH (an aqueous tetramethylammonium hydroxide solution) is being used for general purposes.
Also, due to miniaturization of a semiconductor device, the trend is moving toward a shorter wavelength of the exposure light source and a higher numerical aperture (higher NA) of the projection lens, and an exposure machine using an ArF excimer laser with a wavelength of 193 nm as a light source has been developed at present. Furthermore, for example, a so-called immersion method of filling a high refractive-index liquid (hereinafter sometimes referred to as an “immersion liquid”) between the projection lens and the sample, and MN lithography of performing exposure to ultraviolet light having a shorter wavelength (13.5 nm) have been proposed.
However, it is actually very difficult to find out an appropriate combination of a resist composition, a developer, a rinsing solution and the like, which is necessary for forming a pattern having overall good performance, and more improvements are demanded. In particular, as the resolved line width of the resist becomes finer, improvement of the line edge roughness performance of a line pattern and the in-plane uniformity of the pattern dimension are required.
On the other hand, as well as the currently predominant positive resist, a negative chemical amplification resist composition for use in the pattern formation by alkali development is also being developed (see, for example, JP-A-2006-317803 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2006-259582, JP-A-2006-195050 and JP-A-2000-206694). Because, in the production of a semiconductor device or the like, patterns having various profiles such as line, trench and hole need to be formed, nevertheless, some patterns are difficult to form by the current positive resist composition.
The pattern formation by alkali development using a conventional negative resist composition readily involves problems such as increase in the line width variation (LWR) or decrease in the focus latitude (DOF), for which swelling at the development is presumed to be a main cause.
Also, a double developing technique as a double patterning technology for further raising the resolution is described in JP-A-2008-292975. By making use of a property that when exposed, the polarity of a resin in a resist composition becomes high in a high light intensity region and is kept low in a low light intensity region, the high exposure region of a specific resist film is dissolved with a high-polarity developer and the low exposure region is dissolved with an organic solvent-containing developer, whereby the medium exposure dose region is allowed to remain without being dissolved/removed by the development and a line-and-space pattern having a pitch half the pitch of the exposure mask is formed.